The present invention relates to a biosensor designed to quickly quantify with ease and high accuracy a specific component in various kinds of sample liquids, and a manufacturing method of the biosensor.
2. Description of the Prior Art
Various kinds of biosensors utilizing the specific catalytic effect of an enzyme have been developed in the past years, but a more accurate one is desired.
An example of the biosensor of the aforementioned type, namely, a glucose sensor applied in the clinical field will be depicted below.
Conventionally, blood plasma obtained from the blood of a patient has been centrifugated and measured in order to quantify glucose included in the blood. This method requires time and labor. Therefore, such a sensor that can measure the concentration of glucose within the blood with use of the whole blood is necessitated.
As a simple glucose sensor, one similar to a test paper used for inspection of urea has been provided. This glucose sensor has a stick-like supporting body and a carrier fixed to the supporting body which includes an enzyme reacting only to glucose and a coloring matter changed by the substance resulting from the enzyme reaction. When the blood is dropped onto the carrier of the sensor and the change of the coloring matter after a predetermined time is measured by the naked eye or by an optical means, the amount of glucose in the blood can be known. According. to the quantifying method using the glucose sensor of this type, however, the result is greatly influenced by the coloring matter in the blood, and therefore the measuring accuracy of the method is low.
According to a different method, a specific component of a living sample such as blood or the like can be quantified with high accuracy without requiring dilution or stirring of the sample liquid. An example of a biosensor executing the above method is proposed in Japanese Patent Laid-open Publication Tokkaihei 1-212345 (212345/1989), which will be discussed below.
The biosensor has an electrode system formed on an insulating base plate by screen printing or the like method, and an enzyme reaction layer which consists of a hydrophilic polymer layer, a oxidoreductase and an electron acceptor is formed on the electrode system.
The biosensor of the above structure operates in a manner as follows. When a sample liquid is dropped on the enzyme reaction layer, the oxidoreductase and electron acceptor are dissolved in the sample liquid, so that the enzyme reaction progresses with a substrate in the sample liquid. As a result, the electron acceptor is reduced. After the enzyme reaction is completed, the reduced electron acceptor is electrochemically oxidized. The concentration of the substrate in the sample liquid is obtained from an oxidization current obtained at this time.
In the conventional biosensor, the working electrode and counter electrode are formed of a material different from that of the insulating layer. Therefore, the reaction layer on the electrode system mainly consisting of the working electrode and counter electrode is formed in conformity with the configuration of the counter electrode. Since the counter electrode of the conventional biosensor is polygonal and mainly square, the reaction layer is apt to be separated from a corner of the counter electrode.